As a ligand, a Group 4 transition metal compound that has one or two cyclopentadienyl groups may be activated by using methyl aluminoxane or a boron compound to be used as a catalyst in olefin polymerization (U.S. Pat. No. 5,580,939; Macromol. Chem. Phys. vol. 197, 1996 3707-3945). This catalyst shows an intrinsic characteristic that is not realized by a known Ziegler-Natta catalyst.
That is, in the polymer that is obtained by using this catalyst, the molecular weight distribution is narrow, the reactivity to a second monomer such as alpha olefins or cyclic olefins is good, and a second monomer distribution of the polymer is uniform. In addition, by changing a substituent of a cyclopentadienyl ligand in a metallocene catalyst, when alpha olefins are polymerized, stereo selectivity of the polymer may be controlled (Angew. Chem. Int. Ed. Engl. 1995, 34, 1143), and when ethylene and another olefin are copolymerized, the degree of copolymerization, a molecular weight, a second monomer distribution and the like may be easily controlled (U.S. Pat. No. 5,470,811).
In accordance with the development of a catalyst system, effort has been continuously made to find a catalyst that is useful to produce LLDPE, VLDPE, EPM, and EPDM that are a copolymer of ethylene and alpha olefins, cyclic olefin copolymers (COC) that are a copolymer of ethylene and cyclic olefins or alpha olefins and cyclic olefins, and a copolymer of ethylene and alpha olefins and styrene. Conditions of the catalyst required to produce the above products comprise excellent activity, high reactivity to second monomers, and the production of polymers having the uniform distribution of second monomers.
Meanwhile, since the metallocene catalyst is expensive as compared to the known Ziegler-Natta catalyst, it is economic when the activity is excellent. If the reactivity to second monomers is good, even though a small amount of second monomers is added, a polymer that comprises a great amount of second monomers may be obtained.
Many researchers have studied various catalysts, resulting in the finding that a bridged catalyst has good reactivity to second monomers. According to the study by F. J. Karol, in order to produce LLDPE products having the density of 0.93 g/cc using hexene as a second monomer, in the case of the bridged catalyst, a ratio of ethylene and hexene may be in the range of 0.004˜0.005, but in the case of the non-bridged catalyst, it is required that the ratio is 0.02 (1997 Apr. 18. US Palm Coast, Fla., Polymer Reaction Engineering Foundation Conference).
In addition, the bridged catalyst has been actively studied because a molecular structure of a propylene polymer may be controlled according to the symmetry of the molecules thereof. Therefore, in order to produce the above copolymer, the bridged catalyst has been watched with interest.
The bridged catalyst that has been studied until now may be roughly classified into three categories according to the shape of bridge. One of them is a catalyst where two cyclopentadienyl ligands are connected by an allylenedibridge according to a reaction of electron-philic body such as alkyl halides and indene or fluorene, second is a silicon-bridged catalyst that is connected by —SiR2—, and third is a methylene-bridged catalyst that is obtained by a reaction of fulbene and indene or fluorene.
JP No. 3823326 suggests that dimethylbis (substituted cyclopentadienyl)silane is produced by reacting substituted cyclopentadiene and dimethyl dihalosilane with each other, and a metallocene compound is produced by reacting dimethylbis (substituted cyclopentadienyl)silane and a halogen compound of a transition metal with each other.
In addition, Korean Patent No. 0746676 suggests a method for producing a metallocene compound that comprises a substituted cyclopentadienyl group and a (substituted)fluorenyl group and has a structure where these groups are bridged by a hydrocarbon group and the like.